The conventional gymnastic apparatus capable of animating a bicycle riding is generally provided with a load adjusting device for increasing or decreasing the magnitude of damping of the rotating wheel. The above-mentioned load adjusting device is generally operated on the mechanical friction or the magnetic damping which is relatively compact and is therefore widely used.
The conventional magnetic damping device comprises a nonmagnetic thin copper piece provided with a U-shaped magnet having thereon a retaining plate which can be located by a retaining device. The retaining plate is further provided with a plurality of retaining teeth. The retaining plate is capable of being actuated by the two cables to rotate. These two cables can be caused to change their relative positions by the rotation of an adjustment button. As the retaining teeth and the retaining device are adjustably engageable at different angles, the U-shaped magnet is caused to bring about the different braking damping effects relative to the thin copper piece. The magnitude of the magnetic damping of the conventional magnetic damping device is dependent on the tooth pitch and the number of teeth of the retaining teeth. As a result, the magnetic damping value of the conventional magnetic damping device is changed in a step-by-step manner. In addition, the retaining teeth and the retaining device of the conventional magnetic damping device are vulnerable to a deadlock caused by an excessively forceful rotation of the addjustment button. Moreover, the efficiency of the gymnastic apparatus is often compromised by the magnet of the conventional magnetic damping device, which can not be automatically controlled in conjunction with the operation of the motor of the gymnastic apparatus.